Thermal properties and tempurature

Question 1

What is thermal expansion and why does it occur

Answer 1

Thermal expansion - when materials are heated, they expand

This occurs because the molecules gain K.E. and start to move around which causes them to spread out (hence expansion)

Question 2

What state expands the most and which expands the least

Answer 2

The most expansion - gas

The least expansion - solid

Question 3

Why does gas expand the most but solid the least

Answer 3

Gases expand the most due to there being no bonds holding the molecules together;
whereas solids only expand slightly due to there being strong bonds holding the molecules together

Question 4

Example of everyday use of thermal expansion

Answer 4

Bimetallic strip in a temperature-activated switch - a metal bar made up of two metals with different rates of expansion

Question 5

When a bi-metallic strip is heated what happens

Answer 5

The two metals expand at different rates causing the bar to bend.

Question 6

What could happen to solid materials when they expand, how can this be stopped

Answer 6

Solids can buckle if they expand too much

To prevent this, gaps are built in between, providing room for expansion.

Question 7

What happens when a substance is heated,

give examples of the things that change

Answer 7

Its physical properties can change

e.g. density and volume
electrical resistance

If these properties change in a well defined way, then you can determine the temperature

Question 8

What is a fixed point

Answer 8

A tempurature where an easily identifiable change occurs

Question 9

How do you build a thermometer

Answer 9

Find out two fixed points on thermometer - 0C (m.p.) and 100C (b.p.)

Equally distribute values between two points using a ruler

Question 10

Describe experiment to show gases expand more than solids

Answer 10

Measure volume of both states at room temperature

Add heat equally to both using water bath

When they are of equal temperature increase

You should expect to see gases expand more than the solid

Question 11

How is linearity achieved in a liquid-in-glass thermometer

Answer 11

Have a tube of uniform diameter

Question 12

Define “linearity” in a thermometer

Answer 12

Getting the same change in length/*C

Question 13

Define “sensitivity”

Answer 13

Change of input/ change in output

How much longer does the column of liquid get/*C of temp increase

Question 14

Define “range”

Answer 14

The lowest and highest temperature readings on the thermometer

Question 15

What is contained in a liquid in glass thermometer

Answer 15

A thin glass capillary tube containing a liquid that expands with temperature

At one end there is a glass bulb, containing a larger volume of the expanding liquid which moves into the capillary tube

Question 16

Why is the capillary tube narrow

Answer 16

So that when the volume expands/contracts by a small percentage there is still a visible change

Question 17

How can sensitivity be increased in a liquid glass thermometer

Answer 17

By using a liquid with a greater co-efficient of expansion

Question 18

What does increasing the size of the bulb do to sensitivity

Answer 18

It increases the sensitivity, but if it is too large it will cause response time to be low as the liquid would take a long time to heat up

Question 19

What is a thermocouple?

Answer 19

A thermocouple is two different types of wire attached together

When the wires are heated, a potential difference occurs

The greater the temperature, the greater the potential difference

Question 20

How does a thermocouple measure tempurature

Answer 20

When the thermal energy increases, the potential difference increases

This is read by looking at a heat-current graph

Question 21

What increases when a substance is heated

Answer 21

Its internal energy increases

the higher the tempurature, the more thermal energy

Question 22

What two energy types are contained in a substance

Answer 22

Kinetic energy - due to the molecules random motion

Potential energy - due to the bonds between the molecules

Question 23

What is the thermal capacity of an object

Answer 23

The required amount of energy to raise the tempurature of a substance by 1*C

This amount of energy is also equal to the amount given out when the substance is cooled by 1*C

Question 24

The greater the thermal capacity of an object…

Answer 24

The more energy it requires to raise its’ tempurature by 1*C

Question 25

Equation for thermal capacity

Answer 25

C = mc
= mass x specific heat capacity
g x j/kg*C

Question 26

Equation for the change in energy

Answer 26

= Mass x Specific heat capacity x Change in tempurature

mc x change in T

Question 27

Give an experiment to measure the specific heat capacity of a substance

Answer 27

1. ) Place a beaker on a balance and press zero
2. ) Add oil to the beaker and measure its mass
3. ) Read the starting temperature of the oil
4. ) Connect a joulemeter to the immersion heater
5. ) Time for 30 minutes
6. ) Read off the number of joules passed through the immersion heater
7. ) Read the final temperature of the oil
8. ) Use the equation - E = MCΔT

Question 28

While a substance changes state why does the temperature remain constant

Answer 28

Because the energy is used to break bonds of the molecules rather than increase its K.E.

Question 29

What is the difference between boiling and evaporation

Answer 29

Boiling occurs at a fixed tempurature and occurs throughout the liquid

Evaporation can occur at any temperature and occurs at the surface of the liquid

Question 30

What is latent heat

Answer 30

The required amount of energy to change to state of a substance

This energy is required to break bonds holding molecules together

Question 31

What is latent heat of fusion

Answer 31

The required energy to change a solid into a liquid

Question 32

What is latent heat of vaporization

Answer 32

The required energy to change a liquid into a gas

Question 33

Equation for latent heat

Answer 33

E = ml

Question 34

Definition of melting point

Answer 34

The tempurature at which a solid changes into a liquid

Question 35

Definition of boiling point

Answer 35

The tempurature at which a liquid changes into a gas

Question 36

Describe an experiment to determine the latent heat of water

Answer 36

Use electrical heater to melt ice for 5 minutes

The electrical energy used is calculated by multiplying the power of electrical heater by time

The mass of water melted is recorded, and the relationship between energy input and mass is calculated

The latent heat is determined by using the equation E=ml